Eight Big Medical and Science Trends to Watch in 2021
The world as we know it has forever changed. With a greater focus on science and technology than before, experts in the biotech and life sciences spaces are grappling with what comes next as SARS-CoV-2, the coronavirus that causes the COVID-19 illness, has spread and mutated across the world.
Even with vaccines being distributed, so much still remains unknown.
Jared Auclair, Technical Supervisor for the Northeastern University's Life Science Testing Center in Burlington, Massachusetts, guides a COVID testing lab that cranks out thousands of coronavirus test results per day. His lab is also focused on monitoring the quality of new cell and gene therapy products coming to the market.
Here are trends Auclair and other experts are watching in 2021.
Better Diagnostic Testing for COVID
Expect improvements in COVID diagnostic testing and the ability to test at home.
There are currently three types of coronavirus tests. The molecular test—also known as the RT-PCR test, detects the virus's genetic material, and is highly accurate, but it can take days to receive results. There are also antibody tests, done through a blood draw, designed to test whether you've had COVID in the past. Finally, there's the quick antigen test that isn't as accurate as the PCR test, but can identify if people are going to infect others.
Last month, Lucira Health secured the U.S. FDA Emergency Use Authorization for the first prescription molecular diagnostic test for COVID-19 that can be performed at home. On December 15th, the Ellume Covid-19 Home Test received authorization as the first over-the-counter COVID-19 diagnostic antigen test that can be done at home without a prescription. The test uses a nasal swab that is connected to a smartphone app and returns results in 15-20 minutes. Similarly, the BinaxNOW COVID-19 Ag Card Home Test received authorization on Dec. 16 for its 15-minute antigen test that can be used within the first seven days of onset of COIVD-19 symptoms.
Home testing has the possibility to impact the pandemic pretty drastically, Auclair says, but there are other considerations: the type and timing of test that is administered, how expensive is the test (and if it is financially feasible for the general public) and the ability of a home test taker to accurately administer the test.
"The vaccine roll-out will not eliminate the need for testing until late 2021 or early 2022."
Ideally, everyone would frequently get tested, but that would mean the cost of a single home test—which is expected to be around $30 or more—would need to be much cheaper, more in the $5 range.
Auclair expects "innovations in the diagnostic space to explode" with the need for more accurate, inexpensive, quicker COVID tests. Auclair foresees innovations to be at first focused on COVID point-of-care testing, but he expects improvements within diagnostic testing for other types of viruses and diseases too.
"We still need more testing to get the pandemic under control, likely over the next 12 months," Auclair says. "The vaccine roll-out will not eliminate the need for testing until late 2021 or early 2022."
Rise of mRNA-based Vaccines and Therapies
A year ago, vaccines weren't being talked about like they are today.
"But clearly vaccines are the talk of the town," Auclair says. "The reason we got a vaccine so fast was there was so much money thrown at it."
A vaccine can take more than 10 years to fully develop, according to the World Economic Forum. Prior to the new COVID vaccines, which were remarkably developed and tested in under a year, the fastest vaccine ever made was for mumps -- and it took four years.
"Normally you have to produce a protein. This is typically done in eggs. It takes forever," says Catherine Dulac, a neuroscientist and developmental biologist at Harvard University who won the 2021 Breakthrough Prize in Life Sciences. "But an mRNA vaccine just enabled [us] to skip all sorts of steps [compared with burdensome conventional manufacturing] and go directly to a product that can be injected into people."
Non-traditional medicines based on genetic research are in their infancy. With mRNA-based vaccines hitting the market for the first time, look for more vaccines to be developed for whatever viruses we don't currently have vaccines for, like dengue virus and Ebola, Auclair says.
"There's a whole bunch of things that could be explored now that haven't been thought about in the past," Auclair says. "It could really be a game changer."
Vaccine Innovation over the last 140 years.
Max Roser/Our World in Data (Creative Commons license)
Advancements in Cell and Gene Therapies
CRISPR, a type of gene editing, is going to be huge in 2021, especially after the Nobel Prize in Chemistry was awarded to Emmanuelle Charpentier and Jennifer Doudna in October for pioneering the technology.
Right now, CRISPR isn't completely precise and can cause deletions or rearrangements of DNA.
"It's definitely not there yet, but over the next year it's going to get a lot closer and you're going to have a lot of momentum in this space," Auclair says. "CRISPR is one of the technologies I'm most excited about and 2021 is the year for it."
Gene therapies are typically used on rare genetic diseases. They work by replacing the faulty dysfunctional genes with corrected DNA codes.
"Cell and gene therapies are really where the field is going," Auclair says. "There is so much opportunity....For the first time in our life, in our existence as a species, we may actually be able to cure disease by using [techniques] like gene editing, where you cut in and out of pieces of DNA that caused a disease and put in healthy DNA," Auclair says.
For example, Spinal Muscular Atrophy is a rare genetic disorder that leads to muscle weakness, paralysis and death in children by age two. As of last year, afflicted children can take a gene therapy drug called Zolgensma that targets the missing or nonworking SMN1 gene with a new copy.
Another recent breakthrough uses gene editing for sickle cell disease. Victoria Gray, a mom from Mississippi who was exclusively followed by NPR, was the first person in the United States to be successfully treated for the genetic disorder with the help of CRISPR. She has continued to improve since her landmark treatment on July 2, 2019 and her once-debilitating pain has greatly eased.
"This is really a life-changer for me," she told NPR. "It's magnificent."
"You are going to see bigger leaps in gene therapies."
Look out also for improvements in cell therapies, but on a much lesser scale.
Cell therapies remove immune cells from a person or use cells from a donor. The cells are modified or cultured in lab, multiplied by the millions and then injected back into patients. These include stem cell therapies as well as CAR-T cell therapies, which are typically therapies of last resort and used in cancers like leukemia, Auclair says.
"You are going to see bigger leaps in gene therapies," Auclair says. "It's being heavily researched and we understand more about how to do gene therapies. Cell therapies will lie behind it a bit because they are so much more difficult to work with right now."
More Monoclonal Antibody Therapies
Look for more customized drugs to personalize medicine even more in the biotechnology space.
In 2019, the FDA anticipated receiving more than 200 Investigational New Drug (IND) applications in 2020. But with COVID, the number of INDs skyrocketed to 6,954 applications for the 2020 fiscal year, which ended September 30, 2020, according to the FDA's online tracker. Look for antibody therapies to play a bigger role.
Monoclonal antibodies are lab-grown proteins that mimic or enhance the immune system's response to fight off pathogens, like viruses, and they've been used to treat cancer. Now they are being used to treat patients with COVID-19.
President Donald Trump received a monoclonal antibody cocktail, called REGEN-COV2, which later received FDA emergency use authorization.
A newer type of monoclonal antibody therapy is Antibody-Drug Conjugates, also called ADCs. It's something we're going to be hearing a lot about in 2021, Auclair says.
"Antibody-Drug Conjugates is a monoclonal antibody with a chemical, we consider it a chemical warhead on it," Auclair says. "The monoclonal antibody binds to a specific antigen in your body or protein and delivers a chemical to that location and kills the infected cell."
Moving Beyond Male-Centric Lab Testing
Scientific testing for biology has, until recently, focused on testing males. Dulac, a Howard Hughes Medical Investigator and professor of molecular and cellular biology at Harvard University, challenged that idea to find brain circuitry behind sex-specific behaviors.
"For the longest time, until now, all the model systems in biology, are male," Dulac says. "The idea is if you do testing on males, you don't need to do testing on females."
Clinical models are done in male animals, as well as fundamental research. Because biological research is always done on male models, Dulac says the outcomes and understanding in biology is geared towards understanding male biology.
"All the drugs currently on the market and diagnoses of diseases are biased towards the understanding of male biology," Dulac says. "The diagnostics of diseases is way weaker in women than men."
That means the treatment isn't necessarily as good for women as men, she says, including what is known and understood about pain medication.
"So pain medication doesn't work well in women," Dulac says. "It works way better in men. It's true for almost all diseases that I know. Why? because you have a science that is dominated by males."
Although some in the scientific community challenge that females are not interesting or too complicated with their hormonal variations, Dulac says that's simply not true.
"There's absolutely no reason to decide 50% of life forms are interesting and the other 50% are not interesting. What about looking at both?" says Dulac, who was awarded the $3 million Breakthrough Prize in Life Sciences in September for connecting specific neural mechanisms to male and female parenting behaviors.
Disease Research on Single Cells
To better understand how diseases manifest in the body's cell and tissues, many researchers are looking at single-cell biology. Cells are the most fundamental building blocks of life. Much still needs to be learned.
"A remarkable development this year is the massive use of analysis of gene expression and chromosomal regulation at the single-cell level," Dulac says.
Much is focused on the Human Cell Atlas (HCA), a global initiative to map all cells in healthy humans and to better identify which genes associated with diseases are active in a person's body. Most estimates put the number of cells around 30 trillion.
Dulac points to work being conducted by the Cell Census Network (BICCN) Brain Initiative, an initiative by the National Institutes of Health to come up with an atlas of cell types in mouse, human and non-human primate brains, and the Chan Zuckerberg Initiative's funding of single-cell biology projects, including those focused on single-cell analysis of inflammation.
"Our body and our brain are made of a large number of cell types," Dulac says. "The ability to explore and identify differences in gene expression and regulation in massively multiplex ways by analyzing millions of cells is extraordinarily important."
Converting Plastics into Food
Yep, you heard it right, plastics may eventually be turned into food. The Defense Advanced Research Projects Agency, better known as DARPA, is funding a project—formally titled "Production of Macronutrients from Thermally Oxo-Degraded Wastes"—and asking researchers how to do this.
"When I first heard about this challenge, I thought it was absolutely absurd," says Dr. Robert Brown, director of the Bioeconomy Institute at Iowa State University and the project's principal investigator, who is working with other research partners at the University of Delaware, Sandia National Laboratories, and the American Institute of Chemical Engineering (AIChE)/RAPID Institute.
But then Brown realized plastics will slowly start oxidizing—taking in oxygen—and microorganisms can then consume it. The oxidation process at room temperature is extremely slow, however, which makes plastics essentially not biodegradable, Brown says.
That changes when heat is applied at brick pizza oven-like temperatures around 900-degrees Fahrenheit. The high temperatures get compounds to oxidize rapidly. Plastics are synthetic polymers made from petroleum—large molecules formed by linking many molecules together in a chain. Heated, these polymers will melt and crack into smaller molecules, causing them to vaporize in a process called devolatilization. Air is then used to cause oxidation in plastics and produce oxygenated compounds—fatty acids and alcohols—that microorganisms will eat and grow into single-cell proteins that can be used as an ingredient or substitute in protein-rich foods.
"The caveat is the microorganisms must be food-safe, something that we can consume," Brown says. "Like supplemental or nutritional yeast, like we use to brew beer and to make bread or is used in Australia to make Vegemite."
What do the microorganisms look like? For any home beer brewers, it's the "gunky looking stuff you'd find at the bottom after the fermentation process," Brown says. "That's cellular biomass. Like corn grown in the field, yeast or other microorganisms like bacteria can be harvested as macro-nutrients."
Brown says DARPA's ReSource program has challenged all the project researchers to find ways for microorganisms to consume any plastics found in the waste stream coming out of a military expeditionary force, including all the packaging of food and supplies. Then the researchers aim to remake the plastic waste into products soldiers can use, including food. The project is in the first of three phases.
"We are talking about polyethylene, polypropylene, like PET plastics used in water bottles and converting that into macronutrients that are food," says Brown.
Renewed Focus on Climate Change
The Union of Concerned Scientists say carbon dioxide levels are higher today than any point in at least 800,000 years.
"Climate science is so important for all of humankind. It is critical because the quality of life of humans on the planet depends on it."
Look for technology to help locate large-scale emitters of carbon dioxide, including sensors on satellites and artificial intelligence to optimize energy usage, especially in data centers.
Other technologies focus on alleviating the root cause of climate change: emissions of heat-trapping gasses that mainly come from burning fossil fuels.
Direct air carbon capture, an emerging effort to capture carbon dioxide directly from ambient air, could play a role.
The technology is in the early stages of development and still highly uncertain, says Peter Frumhoff, director of science and policy at Union of Concerned Scientists. "There are a lot of questions about how to do that at sufficiently low costs...and how to scale it up so you can get carbon dioxide stored in the right way," he says, and it can be very energy intensive.
One of the oldest solutions is planting new forests, or restoring old ones, which can help convert carbon dioxide into oxygen through photosynthesis. Hence the Trillion Trees Initiative launched by the World Economic Forum. Trees are only part of the solution, because planting trees isn't enough on its own, Frumhoff says. That's especially true, since 2020 was the year that human-made, artificial stuff now outweighs all life on earth.
More research is also going into artificial photosynthesis for solar fuels. The U.S. Department of Energy awarded $100 million in 2020 to two entities that are conducting research. Look also for improvements in battery storage capacity to help electric vehicles, as well as back-up power sources for solar and wind power, Frumhoff says.
Another method to combat climate change is solar geoengineering, also called solar radiation management, which reflects sunlight back to space. The idea stems from a volcanic eruption in 1991 that released a tremendous amount of sulfate aerosol particles into the stratosphere, reflecting the sunlight away from Earth. The planet cooled by a half degree for nearly a year, Frumhoff says. However, he acknowledges, "there's a lot of things we don't know about the potential impacts and risks" involved in this controversial approach.
Whatever the approach, scientific solutions to climate change are attracting renewed attention. Under President Trump, the White House Office of Science and Technology Policy didn't have an acting director for almost two years. Expect that to change when President-elect Joe Biden takes office.
"Climate science is so important for all of humankind," Dulac says. "It is critical because the quality of life of humans on the planet depends on it."
Jamie Rettinger was still in his thirties when he first noticed a tiny streak of brown running through the thumbnail of his right hand. It slowly grew wider and the skin underneath began to deteriorate before he went to a local dermatologist in 2013. The doctor thought it was a wart and tried scooping it out, treating the affected area for three years before finally removing the nail bed and sending it off to a pathology lab for analysis.
"I have some bad news for you; what we removed was a five-millimeter melanoma, a cancerous tumor that often spreads," Jamie recalls being told on his return visit. "I'd never heard of cancer coming through a thumbnail," he says. None of his doctors had ever mentioned it either. "I just thought I was being treated for a wart." But nothing was healing and it continued to bleed.
A few months later a surgeon amputated the top half of his thumb. Lymph node biopsy tested negative for spread of the cancer and when the bandages finally came off, Jamie thought his medical issues were resolved.
Melanoma is the deadliest form of skin cancer. About 85,000 people are diagnosed with it each year in the U.S. and more than 8,000 die of the cancer when it spreads to other parts of the body, according to the Centers for Disease Control and Prevention (CDC).
There are two peaks in diagnosis of melanoma; one is in younger women ages 30-40 and often is tied to past use of tanning beds; the second is older men 60+ and is related to outdoor activity from farming to sports. Light-skinned people have a twenty-times greater risk of melanoma than do people with dark skin.
"When I graduated from medical school, in 2005, melanoma was a death sentence" --Diwakar Davar.
Jamie had a follow up PET scan about six months after his surgery. A suspicious spot on his lung led to a biopsy that came back positive for melanoma. The cancer had spread. Treatment with a monoclonal antibody (nivolumab/Opdivo®) didn't prove effective and he was referred to the UPMC Hillman Cancer Center in Pittsburgh, a four-hour drive from his home in western Ohio.
An alternative monoclonal antibody treatment brought on such bad side effects, diarrhea as often as 15 times a day, that it took more than a week of hospitalization to stabilize his condition. The only options left were experimental approaches in clinical trials.
Early research
"When I graduated from medical school, in 2005, melanoma was a death sentence" with a cure rate in the single digits, says Diwakar Davar, 39, an oncologist at UPMC Hillman Cancer Center who specializes in skin cancer. That began to change in 2010 with introduction of the first immunotherapies, monoclonal antibodies, to treat cancer. The antibodies attach to PD-1, a receptor on the surface of T cells of the immune system and on cancer cells. Antibody treatment boosted the melanoma cure rate to about 30 percent. The search was on to understand why some people responded to these drugs and others did not.
At the same time, there was a growing understanding of the role that bacteria in the gut, the gut microbiome, plays in helping to train and maintain the function of the body's various immune cells. Perhaps the bacteria also plays a role in shaping the immune response to cancer therapy.
One clue came from genetically identical mice. Animals ordered from different suppliers sometimes responded differently to the experiments being performed. That difference was traced to different compositions of their gut microbiome; transferring the microbiome from one animal to another in a process known as fecal transplant (FMT) could change their responses to disease or treatment.
When researchers looked at humans, they found that the patients who responded well to immunotherapies had a gut microbiome that looked like healthy normal folks, but patients who didn't respond had missing or reduced strains of bacteria.
Davar and his team knew that FMT had a very successful cure rate in treating the gut dysbiosis of Clostridioides difficile, a persistant intestinal infection, and they wondered if a fecal transplant from a patient who had responded well to cancer immunotherapy treatment might improve the cure rate of patients who did not originally respond to immunotherapies for melanoma.
The ABCDE of melanoma detection
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Clinical trial
"It was pretty weird, I was totally blasted away. Who had thought of this?" Jamie first thought when the hypothesis was explained to him. But Davar's explanation that the procedure might restore some of the beneficial bacterial his gut was lacking, convinced him to try. He quickly signed on in October 2018 to be the first person in the clinical trial.
Fecal donations go through the same safety procedures of screening for and inactivating diseases that are used in processing blood donations to make them safe for transfusion. The procedure itself uses a standard hollow colonoscope designed to screen for colon cancer and remove polyps. The transplant is inserted through the center of the flexible tube.
Most patients are sedated for procedures that use a colonoscope but Jamie doesn't respond to those drugs: "You can't knock me out. I was watching them on the TV going up my own butt. It was kind of unreal at that point," he says. "There were about twelve people in there watching because no one had seen this done before."
A test two weeks after the procedure showed that the FMT had engrafted and the once-missing bacteria were thriving in his gut. More importantly, his body was responding to another monoclonal antibody (pembrolizumab/Keytruda®) and signs of melanoma began to shrink. Every three months he made the four-hour drive from home to Pittsburgh for six rounds of treatment with the antibody drug.
"We were very, very lucky that the first patient had a great response," says Davar. "It allowed us to believe that even though we failed with the next six, we were on the right track. We just needed to tweak the [fecal] cocktail a little better" and enroll patients in the study who had less aggressive tumor growth and were likely to live long enough to complete the extensive rounds of therapy. Six of 15 patients responded positively in the pilot clinical trial that was published in the journal Science.
Davar believes they are beginning to understand the biological mechanisms of why some patients initially do not respond to immunotherapy but later can with a FMT. It is tied to the background level of inflammation produced by the interaction between the microbiome and the immune system. That paper is not yet published.
Surviving cancer
It has been almost a year since the last in his series of cancer treatments and Jamie has no measurable disease. He is cautiously optimistic that his cancer is not simply in remission but is gone for good. "I'm still scared every time I get my scans, because you don't know whether it is going to come back or not. And to realize that it is something that is totally out of my control."
"It was hard for me to regain trust" after being misdiagnosed and mistreated by several doctors he says. But his experience at Hillman helped to restore that trust "because they were interested in me, not just fixing the problem."
He is grateful for the support provided by family and friends over the last eight years. After a pause and a sigh, the ruggedly built 47-year-old says, "If everyone else was dead in my family, I probably wouldn't have been able to do it."
"I never hesitated to ask a question and I never hesitated to get a second opinion." But Jamie acknowledges the experience has made him more aware of the need for regular preventive medical care and a primary care physician. That person might have caught his melanoma at an earlier stage when it was easier to treat.
Davar continues to work on clinical studies to optimize this treatment approach. Perhaps down the road, screening the microbiome will be standard for melanoma and other cancers prior to using immunotherapies, and the FMT will be as simple as swallowing a handful of freeze-dried capsules off the shelf rather than through a colonoscopy. Earlier this year, the Food and Drug Administration approved the first oral fecal microbiota product for C. difficile, hopefully paving the way for more.
An older version of this hit article was first published on May 18, 2021
All organisms have the capacity to repair or regenerate tissue damage. None can do it better than salamanders or newts, which can regenerate an entire severed limb.
That feat has amazed and delighted man from the dawn of time and led to endless attempts to understand how it happens – and whether we can control it for our own purposes. An exciting new clue toward that understanding has come from a surprising source: research on the decline of cells, called cellular senescence.
Senescence is the last stage in the life of a cell. Whereas some cells simply break up or wither and die off, others transition into a zombie-like state where they can no longer divide. In this liminal phase, the cell still pumps out many different molecules that can affect its neighbors and cause low grade inflammation. Senescence is associated with many of the declining biological functions that characterize aging, such as inflammation and genomic instability.
Oddly enough, newts are one of the few species that do not accumulate senescent cells as they age, according to research over several years by Maximina Yun. A research group leader at the Center for Regenerative Therapies Dresden and the Max Planck Institute of Molecular and Cell Biology and Genetics, in Dresden, Germany, Yun discovered that senescent cells were induced at some stages of regeneration of the salamander limb, “and then, as the regeneration progresses, they disappeared, they were eliminated by the immune system,” she says. “They were present at particular times and then they disappeared.”
Senescent cells added to the edges of the wound helped the healthy muscle cells to “dedifferentiate,” essentially turning back the developmental clock of those cells into more primitive states.
Previous research on senescence in aging had suggested, logically enough, that applying those cells to the stump of a newly severed salamander limb would slow or even stop its regeneration. But Yun stood that idea on its head. She theorized that senescent cells might also play a role in newt limb regeneration, and she tested it by both adding and removing senescent cells from her animals. It turned out she was right, as the newt limbs grew back faster than normal when more senescent cells were included.
Senescent cells added to the edges of the wound helped the healthy muscle cells to “dedifferentiate,” essentially turning back the developmental clock of those cells into more primitive states, which could then be turned into progenitors, a cell type in between stem cells and specialized cells, needed to regrow the muscle tissue of the missing limb. “We think that this ability to dedifferentiate is intrinsically a big part of why salamanders can regenerate all these very complex structures, which other organisms cannot,” she explains.
Yun sees regeneration as a two part problem. First, the cells must be able to sense that their neighbors from the lost limb are not there anymore. Second, they need to be able to produce the intermediary progenitors for regeneration, , to form what is missing. “Molecularly, that must be encoded like a 3D map,” she says, otherwise the new tissue might grow back as a blob, or liver, or fin instead of a limb.
Wound healing
Another recent study, this time at the Mayo Clinic, provides evidence supporting the role of senescent cells in regeneration. Looking closely at molecules that send information between cells in the wound of a mouse, the researchers found that senescent cells appeared near the start of the healing process and then disappeared as healing progressed. In contrast, persistent senescent cells were the hallmark of a chronic wound that did not heal properly. The function and significance of senescence cells depended on both the timing and the context of their environment.
The paper suggests that senescent cells are not all the same. That has become clearer as researchers have been able to identify protein markers on the surface of some senescent cells. The patterns of these proteins differ for some senescent cells compared to others. In biology, such physical differences suggest functional differences, so it is becoming increasingly likely there are subsets of senescent cells with differing functions that have not yet been identified.
There are disagreements within the research community as to whether newts have acquired their regenerative capacity through a unique evolutionary change, or if other animals, including humans, retain this capacity buried somewhere in their genes.
Scientists initially thought that senescent cells couldn’t play a role in regeneration because they could no longer reproduce, says Anthony Atala, a practicing surgeon and bioengineer who leads the Wake Forest Institute for Regenerative Medicine in North Carolina. But Yun’s study points in the other direction. “What this paper shows clearly is that these cells have the potential to be involved in tissue regeneration [in newts]. The question becomes, will these cells be able to do the same in humans.”
As our knowledge of senescent cells increases, Atala thinks we need to embrace a new analogy to help understand them: humans in retirement. They “have acquired a lot of wisdom throughout their whole life and they can help younger people and mentor them to grow to their full potential. We're seeing the same thing with these cells,” he says. They are no longer putting energy into their own reproduction, but the signaling molecules they secrete “can help other cells around them to regenerate.”
There are disagreements within the research community as to whether newts have acquired their regenerative capacity through a unique evolutionary change, or if other animals, including humans, retain this capacity buried somewhere in their genes. If so, it seems that our genes are unable to express this ability, perhaps as part of a tradeoff in acquiring other traits. It is a fertile area of research.
Dedifferentiation is likely to become an important process in the field of regenerative medicine. One extreme example: a lab has been able to turn back the clock and reprogram adult male skin cells into female eggs, a potential milestone in reproductive health. It will be more difficult to control just how far back one wishes to go in the cell's dedifferentiation – part way or all the way back into a stem cell – and then direct it down a different developmental pathway. Yun is optimistic we can learn these tricks from newts.
Senolytics
A growing field of research is using drugs called senolytics to remove senescent cells and slow or even reverse disease of aging.
“Senolytics are great, but senolytics target different types of senescence,” Yun says. “If senescent cells have positive effects in the context of regeneration, of wound healing, then maybe at the beginning of the regeneration process, you may not want to take them out for a little while.”
“If you look at pretty much all biological systems, too little or too much of something can be bad, you have to be in that central zone” and at the proper time, says Atala. “That's true for proteins, sugars, and the drugs that you take. I think the same thing is true for these cells. Why would they be different?”
Our growing understanding that senescence is not a single thing but a variety of things likely means that effective senolytic drugs will not resemble a single sledge hammer but more a carefully manipulated scalpel where some types of senescent cells are removed while others are added. Combinations and timing could be crucial, meaning the difference between regenerating healthy tissue, a scar, or worse.